that's the one, need allen wrench to remove itIf the one you describe looks like the one in my picture, no one seems to know much. I have only ever seen this nut used on the mailtruck that were manufactured into 1932 after normal production run ended. This is the one on my unrestored ‘31 mail truck
Has Allen passed on, or is he still making wrenches?that's the one, need allen wrench to remove it